Various display systems have been used over the years to generate images. Such display systems may employ image devices, such as cathode ray tubes (CRTs), liquid crystal displays (LCDs), or electrically addressed emissive displays, e.g. plasma displays. The display systems further may incorporate a passive display screen or an active display screen.
Many of today's display systems transmit successive images having differing characteristics, such as different colors. A standard series of colored images associated with a final composite image may be transmitted at a rate that is sufficiently fast that the human eye perceives an image that is a combination of the separately colored images. Such a system may be referred to as a field-sequential display system. One such system includes a light source, a color wheel, and a spatial light modulator. Light generated from the light source in such a display system is directed onto the color wheel, which sequentially filters light from the light source, typically producing red light, green light, blue light, and depending upon the filter, white (unfiltered) light. These colored lights thus typically are sent sequentially to the spatial light modulator, which modulates each of the colored lights as required to achieve the desired image.
Color wheels typically may be planar, cylindrical or conical in shape. Color wheels have transitions between filters, that may be referred to as spokes, that extend normal to the direction of travel of the filters. When a spoke intersects the light beam, this produces a filtered light beam that has two colors. This mixed light is often discarded by the display system, in order to produce colored images that are only one of the three primary colors or white. In one existing projector, the light beam is circular in transverse cross section and occupies a 17-degree arc for each of the four spokes of a rotating color wheel. These four spokes of 17 degrees each add up to 68 degrees, or 18 percent, of the available 360 degrees of time-averaged light that may be wasted.